1. Field of the Invention
This invention relates to an image recording apparatus for recording in a dot-matrix form by scanning, for example, an ink jet head in a scan direction relative to a recording medium. In particular, the invention relates to an image recording apparatus that has a plurality of element arrays provided with a plurality of recording elements arranged with a predetermined spacing in a direction approximately perpendicular to the scanning direction.
2. Description of Related Art
Conventionally, an apparatus for recording an image moves a recording head in a scanning direction relative to a recording medium. In this case, the number of recording elements of the recording head in a direction perpendicular to the scanning direction determines a dot density of the image to be printed in a longitudinal direction. For example, recording elements are arranged with a pitch of 1/360 inch in the longitudinal direction in a recording apparatus with a density of 360 dpi (dot/inch). In addition, the length of the recording element array in the longitudinal direction is generally set to a height of a character line to be recorded. That is, approximately one line of text is recorded with one scan.
In conventional image recording apparatus, arranging recording elements in close proximity to each other is necessary to record with high resolution. However, there is physically a limit when arranging recording elements in close proximity to each other. For example, a large number of recording elements, i.e., ink ejecting nozzles, have to be disposed in the longitudinal direction in an ink jet recording head. However, as space between the nozzles becomes small, the small space requires advanced and complicated manufacturing techniques. Thereby, a limit is reached from the viewpoint of manufacturing technique or cost.
It is possible to perform a recording operation with high resolution to some degree by utilizing a recording head 50 as shown in FIG. 7A. The recording head 50 includes a plurality of element arrays (two arrays 50.sub.L1 and 50.sub.L2 are illustrated in FIG. 7A) in a scanning direction X. Each element array 50.sub.L1 and 50.sub.L2 has a plurality of recording elements 50s arranged with a predetermined spacing in a longitudinal direction Y approximately perpendicular to the scanning direction X. In addition, the element arrays 50.sub.L1 and 50.sub.L2 are combined such that each element 50s of one element array 50 is positioned between the elements 50s of the other element array 50. Considering both element arrays 50.sub.L1, and 50.sub.L2 as a unit, it appears that the recording elements 50s are arranged relatively close to each other in the direction of Y with the space between the recording elements 50s kept constant. The recording head 50 is scanned in the scanning direction X while controllably driven to slightly deviate the recording timing of each element array 50.sub.L1 and 50.sub.L2. Thereby, recording is performed with each of the recording elements 50s of both element arrays 50.sub.L1 and 50.sub.L2. As a result, print dots (shown as black circles) are recorded by the one element array 50.sub.L1 and print dots (shown as white circles) are recorded by the other element array 50.sub.L2 as shown in FIG. 7B.
The recording head 50 records by one scanning operation such that the dot lines recorded by the recording elements 50s of the element array 50.sub.L2 are recorded between the dot lines recorded by the recording elements 50s of the element array 50.sub.L1. In this manner, the space between dot lines becomes half the space P between the elements 50s of each element array 50.sub.L1 and 50.sub.L2. However, the positioning precision of print dots is degraded as shown in FIG. 7B because of the adverse effects caused by unevenness of the space D (shown in FIG. 7A) between the element arrays 50.sub.L1 and 50.sub.L2 by the manufacturing error of the recording head 50. Further, the positioning precision of print dots in FIG. 7B is degraded by the repeated fluctuation that microscopically varies the scanning speed of the carriage on which the recording head 50 is mounted. For example, in the case of recording a straight line in the longitudinal direction (i.e., the Y direction), the print dots are recorded in a waveform to form a bold straight line, which degrades recording quality and precision. Therefore, the conventional recording head does not afford enhanced precision, with the result that it is unsuitable for the printing operation that requires high resolution and high precision such as image printing.